1: First of all I checked the logbuffer, the entries in the logbuffer showed that the vlan 70 was getting up/down.2: As the vlan 70 is for the eth-trunk1 (for link between the NE40Es), so I checked the configuration of Eth-trunk1.interface Eth-Trunk1 description TO-FSB-NE40E-B2 portswitch port link-type trunk port trunk allow-pass vlan 50 51 703: I restricted the access to the vlan 50 and vlan 51 on the eth-trunk1, vlan 70 became stable after that.4: Then I allow-pass both the vlans one by one and monitored the state of vlan 70.5: When I allowed vlan 50 the problem started to came up once again, so I restrict it again. and only allow-pass vlan 51 and vlan 70interface Eth-Trunk1 description TO-FSB-NE40E-B2 portswitch port link-type trunk port trunk allow-pass vlan 51 706: The reason was that vlan 50 was generating broadcast packets due to which the eth-trunk1 link became congested so the vlan 70 up/down.

Root Cause

This showed that there might be conjestion on the link due to extra traffic.